Method of making fibrous sheet material



United States Patent Ofice 3,542,910 METHOD OF MAKING FIBROUS SHEET MATERIAL Michael Barash, Rockville Centre, N.Y., and Benedict S.

Anthony, Milford, Pa., assignors to Collagen Corporation, New York, N.Y., a corporation of New York No Drawing. Filed Nov. 25, 1966, Ser. No. 596,742 Int. Cl. D0411 1/64 U.S. Cl. 264-122 18 Claims ABSTRACT OF THE DISCLOSURE This specification relates to reconstituted sheet material having properties at least equal to those of natural leather, said sheet material consisting essentially of leather fibres and polyamide-type synthetic resin fibres held together by a bonding material, the sheet being produced by forming a dry batt of the leather and synthetic resin fibres, applying a bonding material to the batt, setting the bonding material in situ, and then drying the resulting sheet.

The present invention is broadly concerned with a high quality sheet material and with its method of manufacture. The invention is more specifically concerned with such a sheet comprising leather fibres utilized in conjunction with synthetic resin fibres of the polyamide type, the fibres of both types being randomly oriented and bonded together by means of a resin binder substantially uniformly dispersed therethrough.

It is well known in the art to form reconstituted sheets of various materials and by various techniques. Some such reconstituted sheets have in the past included leather. However, the art has not been able to produce sheet material which equalled leather in its primary characteristicssuppleness, breathability or porosity, wear resistance and strength. Moreover, in those prior art sheets which included leather, selectivity usually had to be practiced in the type of leather utilized.

It is a prime object of the present invention to form a sheet including leather fibres which equals or exceeds the original leather in several significant characteristics, such as flexibility, edge and stitch tear strength, dimensional stability even after successive wettings and dryings, breathability and the like. The sheets of the present invention have excellent dimensional stability at elevated temperatures and have excellent stretch fatigue characteristics. Indeed, the reconstituted sheet material of the present invention has characteristics of the types described which equal or exceed those of high quality natural leather. The sheet material of the present invention therefore may be used in place of natural leather in handbags, belts, clothing, shoes and the like, where heretofore only natural leather had practical utility. It may also be used in other and more heavy duty applications, such as in furniture or automobile upholstery.

It is a further prime object of the present invention to produce a reconstituted leather sheet which can utilize all types and grades of leather in the formation thereof. All types of leathers produced from the skin or hide of animal, reptile, fish and birds, as well as all kinds of tannage, such as chrome, vegetable, alum and the like, and all grades of leather such as a top grain layer or splits derived from the lower layer, may be elfectively used in accordance with the present invention. In addition, the present invention can make use of those types and parts of natural leathers which generally are not suitable for use in high quality applications. For example, chrome tanned splits are usually disposed of by the tannery as a waste material, as are those portions of the hide and skin known as trimmings, bellies and flanks; they may, however, be used in accordance with the present invention.

3,542,919 Patented Nov. 24, 1970 By permitting the total utilization of tanned hides and skins, thereby eliminating unnecessary waste, while at the same time producing a sheet material which can be used in applications where formerly only high grade natural leather sheets could be employed, a very significant money saving is accomplished.

In addition, a great saving in labor cost is realized. The

material of the present invention can be produced in a continuous sheet of uniform width, thickness, appearance and quality. This contrasts markedly with natural leather, the individual sheets of which are limited in size and which are non-uniform in thickness and quality. Because of the important uniformity of the product of the present invention semi-skilled or non-skilled labor can be employed for grading and cutting. Dies may be used for cutting many layers at a time, whereas with natural leather each individual layer is generally cut by hand, one at a time. Storage costs are reduced since the material of the present invention can be packed in rolls rather than bundles, and special conditioning equipment is not required, since storage under a wide range of humidity and temperature conditions is feasible without damage to the end product. The sheet material produced in accordance with the present invention is superior to conventional leather in many important respects. Its dimensional stability is better; it will not shrink even though it may be soaked and dried many times over, or permitted to stand for long periods of time. It resists aging, even under normal circumstances, better than natural leather. It has better stitch-tear resistance and edge-tear strength than natural leather. Its flexibility and suppleness and its porosity or breathability are at least as good as natural leather.

The product of the present invention may be employed in conjunction with conventional finishing and embossing methods such as are presently used with natural leathers.

As has been indicated, any type of leather may be employed in conjunction with the present invention. The pieces of leather, of whatever shape, size, type of tannage, etc., are first reduced to individual fibres, which fibres are substantially utilized in the formation of the reconstituted leather sheet. The leather fibres used must be of a certain character before the objectives of the present invention can be attained. They must be of a certain size (thickness and length) and they should have a certain pH characteristic and a certain water content. More specifically, the individual fibres should have a length between .25-1 inch, and a thickness no less than .001 inch and generally between .001-.003 inch. Fibres having a thickness or length substantially less than those specified, if present, add little or nothing to the characteristics of the product and should be avoided. Fibres having a thickness or length substantially greater than that specified likewise are undesirable. Some leather fibres having thickness or length outside the specified ranges may be present, but it is important that the bulk of the fibres have thickness and length within the specified ranges if sheet material having the desired physical characteristics is to be produced.

The pH of the leather fibres is preferably within the range of 5.05.5, and the leather fibres should have a water content within the range of 30-60% by weight.

There are many ways known to the art by means of which leather sheets or scraps can be converted into a fibrous condition, the fibres having desired characteristics of length, thickness, pH and water content. In accordance with one exemplary procedure which is essentially standard insofar as the basic operations which are carried out are concerned, the leather pieces, either sheet, scrap or both, are thoroughly washed to remove contamination and impurities such as dirt, hair and the like. The washed leather is then placed in a paddle wheel drum containing a neutralizing solution of an alkali such as sodium bicarbonate, preferably held at a temperature in the range of about 7085 F. The leather is tumbled in this drum and the pH of the solution is checked and adjusted until the desired pH within the range of 5.0-5.5 is reached.

Attaining the proper pH value for the leather at this stage, which pH value is substantially retained by the leather as it is further processed, is believed to be important in connection with the practice of the present invention. The leather fibres are believed to maintain maximum tensile strength and elongation characteristics under these circumstances. The fibres can be stored over long periods of time without deterioration. Moreover, leather fibres having the specified pH will produce a batt which can more readily be saturated by bonding material.

After the leather has been brought to a proper pH it is dehydrated to such an extent that Water in excess of 50% by weight is removed therefrom. This may be accomplished by a mangle or squeeze rolls. The thus-dehydrated leather is then passed into a temperatureand humiditycontrolled zone where its moisture content is reduced to a range between about -40% by weight. Attaining a proper moisture content for the leather is believed to be important in accomplishing the proper reduction of the leather to fibre in the subsequent steps.

There are many known ways for reducing leather to dry leather fibres. In accordance with one exemplary known procedure, the leather pieces are first cut into narrow strips by a series of rotary disk knives, the strips are further cut to chip form in a second device by means of a series of whirling blades, and the chips are then reduced to fibre length by means of hammermills, the latter devices consisting of a series of rapidly rotating blades which cut the chips and force the material through a perforated screen. The size of the openings in the screen and the activity of the hammermill blades are so designed that the leather fibres, either when they come from the hammermills or after being subjected, if necessary, to a subsequent attrition step, comprise primarily fibres having lengths between .25-1 inch and having a thickness between .001 and .003 inch. Leather fibres having a thickness substantially less than .001 inch are really more in the nature of a powder than in the nature of fibres, and are to be avoided; they tend to reduce the desirable physical characteristics of the finished product. Leather fibres having a thickness substantially greater than .003 inch appear to be too coarse to produce sheets having the desired physical characteristics. The leather fibres will have their natural crimped shape, and when the bulk of the fibres have lengths and thicknesses within the ranges specified they will, when treated as described below, produce sheets having the desired physical characteristics.

In the reduction of the leather to fibrous form nubs or ball-like bundles are found to be present. These nubs are deleterious insofar as the present invention is concerned, and are desirably removed from the fibre mass. One known way in which this can be accomplished is by using an air classification process, a forced current of air separating the heavy nubs from the lighter fibres.

The leather fibres having the characteristics set forth are now ready for use in accordance with the present invention. They may be thus used immediately upon their formation, or they may be stored and drawn from storage when needed. It is important to note that the leather fibres are, at this stage of the procedure, capable of being stored for long periods of time under normal conditions without deterioration.

In order to produce sheets having the exceptional physical characteristics above set forth, synthetic resin fibres of a particular type, to wit, nylon or other synthetic polyamides, are utilized. As with the leather fibres, thickness and fibre length are important characteristics. Thickness must be between .003 inch and .006 inch, with all .of the polyamide fibres employed in a given sheet preferably having essentially the same thickness. The length of the polyamide fibres should be between 1l.5 inch, with an average length of 1.25 inch preferred. It will be understood that this refers to the length of the bulk of the fibres, and that any commercial lot nominally of a given fibre length will almost inevitably contain some fibres with lengths outside the specified value or range of values. The polyamide fibres should be of crimped shape.

The crimped leather and polyamide fibres are thoroughly combined or mixed while dry and are formed into a relatively fluffy batt. This may be done in any one of a number of ways, such as by utilizing a mat-forming machine of the type shown in Langden et al. Pat. 2,890,- 497 of June 16, 1959 entitled Machine for Forming Random Fibre Webs. The required batt may also be formed by superposing webs of leather and polyamide fibres and blending those fibres into a single web by utilizing a needle punching technique such as is Well known in the art. The resultant batt comprises randomly intermixed leather and polyamide fibres formed into a porous, substantially flutfy, dry body, preferably in the form of a continuous sheet.

The proportions of leather fibre and polyamide fibre should lie within specific ranges. The leather fibres should be present in an amount between 5080 parts by weight and the polyamide fibres should be present in an amount between 50-20 parts by weight. Proportions by weight of leather and polyamide fibres of :30 is preferred for most purposes, that proportion producing a sheet having maximum tear and stitch strength. When the leather and polyamide fibres are present in proportions of :20 a sheet is produced which has increased softness, but at a sacrifice in strength.

The density of the batt produced at this stage of the procedure may vary over relatively wide limits, provided only that it is sufiiciently porous so as to permit the subsequently applied bonding material to thoroughly penetrate the batt. Purely by way of example, a batt having a thickness of about /2 inch and a weight of 10 ounces per square yard gives excellent results.

The batt may be, and preferably is, self-sustaining and used as such but, if desired, it may be deposited on a continuous backing sheet such as scrim.

The thus-formed batt is then treated with a bonding agent of particular type, to wit, a water-dispersed acrylic resin, such as that sold by Rohm & Haas under the trade designation 5-1. The bonding agent must thoroughly penetrate the batt, since it functions as the sole means positively securing the blended fibres to one another. This thorough penetration and saturation may be accomplished by causing the batt to become immersed in and move through a bath of such bonding agent, which bath may be a water solution of the acrylic resin containing 17% of such resin. If desired, and as preferred, a wetting agent may also be incorporated into the bath of bonding agent in order to facilitate the penetration of the web thereby. Such a wetting agent may be a dioctyl sodium sulfosuccinate or other anionic sulfonated alkyl ester, such as that sold by Rohm & Haas under the trade designation GR-S. The amount of wetting agent in the bonding agent bath may be on the order of 0.1% based upon the total solids content, but that value can be increased or decreased somewhat in order to compensate for variations in the moisture content of the leather fibres employed.

The batt may, while it is passing through the bonding agent bath, be appropriately manipulated in order to ensure that it is thoroughly saturated with the bonding agent. For example, it may, after immersion, be wrung out and then resaturated, as by being passed between a pair of closely positioned rollers and then permitted to expand.

The batt saturated with acrylic resin bonding material is then subjected to the action of another reagent which fixes or sets the bonding material in situ, while the latter thoroughly saturates the batt and thus secures together adjacent portions of the randomly intermixed leather and polyamide fibres. The reagent involved is an alkali metal halide such as sodium, potassium or zinc chloride, with the latter two being preferred. A 20% water solution of such a reagent may be employed as a bath into which the bonding-agent-saturated batt is immersed.

The batt is then removed from the action of the fixing reagent and rinsed and dried. Before rinsing and drying, however, sufficient time is provided to permit the bonding agent to set and thus bond the fibres to one another. This setting process may be accelerated, if desired, by the application of a moderate amount of heat.

After the bonding material has set the 'batt is rinsed in water and mangled one or more times in order to remove therefrom the excess bonding material, fixing agent and setting agent. Thereafter it is subjected to a heat cure in an oven at a temperature between 350-500 F. for an appropriate period of time, in order to produce a substantially bone dry sheet. A three-minute cure at the 350 F. temperature is usually adequate; a lesser time is required at the 500 F. temperature.

After the sheet is removed from the curing oven it is preferably passed between a pair of embossing rolls which compresses the sheet to a desired uniform thickness within the range of .01.50 inch and produces the desired surface characteristic simulating, if desired, a particular type of natural leather.

The sheet may be treated with oils commonly used in the tanning industry, such as neatsfoot oil, and with any desired dyes, all as is conventional in connection with the treatment of natural leather. The sheet may, after formation, be lacquered, stained, embossed, or otherwise finished so as to adapt it to suitable end product use in shoes, handbags, garments, luggage and the like.

In the practice of the present invention fibres derived from natural leather are mingled or interspersed with fibres of synthetic polyamide materials such as nylon, the fibres being bonded by an acrylic resin bonding material, thereby to produce a reconstituted sheet which attains, and in some instances exceeds, the physical characteris tics of natural leather and in addition exhibits physical properties to which natural leather cannot lay claim, to wit, uniformity of size, thickness and shape, stability in light, heat, etc., resistance to dry and wet rot due to fungi and bacteria, and dimensional stability after repeated wetdry cycles. Significantly, the sheet material of the present invention can be formed by reclaiming leather products formerly discarded as waste. The thus formed sheet can be used in place of high grade natural leathers in such applications as shoes, clothing, upholstery and the l1l e, at great saving in cost and with no loss, and even wlth some gain, in physical properties.

It will be apparent that many of the specific details here disclosed may be varied, all without departing from the spirit of the invention as defined in the following claims.

We claim:

1. A process of forming flexible, breathable nonstretchable sheet material which comprises (1) forming a dry, fiutfy batt of randomly oriented fibres of leather and synthetic polyamides, the bulk of said leather fibres having lengths between .25-1 inch, said leather fibres being present in an amount between 50-80 parts by weight, and said polyamide fibres being present in an amount between 50-20 parts by weight; (2) wetting said batt with a liquid bonding material consisting essentially of acrylic ester; (3) subjecting said wetted batt to the action of a reagent selected from the group consisting of halides of sodium, potassium, and zinc, and mixtures thereof; and (4) drying said batt.

2. The process of claim 1, in which a wetting agent is added to said batt as part of step (2).

3. The process of claim 2, in which said batt is substantially saturated with said bonding material in step (2).

4. The process of claim 1, in which said batt is substantially saturated with said bonding material in step (2).

5. The process of claim 1, in which said polyamide fibres have a length on the order of 1.25 inch.

6. The process of claim 5, in which a wetting agent is added to said batt as part of step (2) 7. The process of claim 5, in which a wetting agent is added to said batt and said batt is substantially saturated with said bonding material, all as part of step (2).

8. The process of claim 1, in which said leather fibres are present substantially in the amount of 70 parts by weight and said polyamide fibres are present substantially in the amount of 30 parts by weight.

9. The process of claim 8, in which a wetting agent is added to said batt and said batt is substantially saturated with said bonding material, all as part of step (2).

10. The process of claim 8, in which said polyamide fibres have a length on the order of 1.25 inch.

11. The process of claim 8, in which said polyamide fibres have a length on the order of 1.25 inch, and in which a wetting agent is added to said batt and said batt is substantially saturated with said bonding material, all as part of step (2).

12. The process of claim 1, in which the leather material, prior to step (1), is treated to have a pH on the order of 5.0-5.5 and a moisture content on the order of 30-40% by weight.

13. The process of claim 12, in which said polyamide fibres have a length on the order of 1.25 inch.

14. The process of claim 12, in which said polyamide fibres have a length on the order of 1.25 inch, and in which a wetting agent is added to said batt and said batt is substantially saturated with said bonding material, all as part of step (2) 15. The process of claim 12, in which said polyamide fibres have a length on the order of 1.25 inch, and in which a wetting agent is added to said batt and in which said batt is immersed in a bath of said bonding material and compressed and released in said bath, thereby to ensure that said =batt is substantially saturated with said bonding material, all as part of step (2) 16. The process of claim 12, in which said leather fibres are present substantially in the amount of 70 parts by weight and said polyamide fibres are present substantially in the amount of 30 parts by weight, and in which said polyamide fibres have a length on the order of 1.25 inch, and in which a wetting agent is added to said batt and said batt is substantially saturated with said bonding material, all as part of step (2).

17. The process of claim 12, in which said leather fibres are present substantially in the amount of 70 parts by weight and said polyamide fibres are present substantially in the amount of 30' parts by weight, and in which said polyamide fibres have a length on the order of 1.25 inch, and in which a wetting agent is added to said batt and in which said 'batt is immersed in a bath of said bonding material and compressed and released in said bath, thereby to ensure that said batt is substantially saturated with said bonding material, all as part of step (2).

18. Process for the manufacture of a composite product which includes leather fibers comprising the steps of (1) treating a leather product in a first zone with an acid solution having a pH of about 5.0 to 5.5 at a temperature in the range of about 70-85 F, -(2) then passing the leather product to a dehydration zone and removing water therein in excess of about 50% by weight, (3) passing the partially dehydrated leather product to a conditioning zone where the moisture content of said product is reduced to 30-40%, (4) thereafter cutting the leather product which includes leather fibres comprising the steps of leather fibers and blending the leather fibers with nonleather fibers, (5) then adding a binding agent to the blend of leather and non-leather fibers, (6) thereafter treating the binding agent and blended fibers with an aldispersed acrylic resin.

References Cited UNITED STATES PATENTS Bergstein 264-322 X Baer 264128 X Waggoner 264-122 van Doosselaere l622 X 3,250,833 5/1966 Wagner 264-428 3,326,740 6/1967 Hand 264128 FOREIGN PATENTS 637,839 3/1962 Canada. 5 664,430 6/1963 Canada.

ROBERT F. WHITE, Primary Examiner A. M. SOKAL, Assistant Examiner 10 U.S. Cl. X.R. 

